Pyometra is defined as an infection in the uterus. The uterus is also known as the womb and is where the developing foetus is located. It is a serious and life threatening condition that must be treated promptly and aggressively.

Pyometra is often the result of hormonal changes in the reproductive tract. Following oestrus ("heat") in the dog, progesterone levels remain elevated for eight to ten weeks and thicken the lining of the uterus in preparation for pregnancy. If pregnancy does not occur for several oestrus cycles, the lining continues to increase in thickness until cysts form within it. The thickened, cystic lining secretes fluids that create an ideal environment in which bacteria can grow. Additionally, high progesterone levels inhibit the ability of the muscles in the wall of the uterus to contract.

Are there other situations that cause the changes in the uterus?

Yes. The use of progesterone-based drugs can do this. In addition, oestrogen will increase the effects of progesterone on the uterus. Drugs containing both hormones are used to treat certain conditions of the reproductive system.

How do bacteria get into the uterus?

The cervix is the gateway to the uterus. It remains tightly closed except during estrus. When it is open, bacteria that are normally found in the vagina can enter the uterus rather easily. If the uterus is normal, the environment is adverse to bacterial survival; however, when the uterine wall is thickened and cystic, perfect conditions exist for bacterial growth. In addition, when these abnormal conditions exist, the muscles of the uterus cannot contract properly. This means that bacteria that enter the uterus cannot be expelled.

When does pyometra occur?

Pyometra may occur in young to middle-aged dogs; however, it is most common in older dogs. After many years of oestrus cycles, the uterine wall undergoes the changes that promote this disease.

The typical time for pyometra to occur is about two to eight weeks after oestrus ("heat cycle").

What are the clinical signs of a dog with pyometra?

The clinical signs depend on whether or not the cervix is open. If it is open, pus will drain from the uterus through the vagina to the outside. It is often noted on the skin or hair under the tail or on bedding and furniture where the dog has laid. Fever, lethargy, anorexia, and depression may or may not be present.

If the cervix is closed, pus that forms is not able to drain to the outside. It collects in the uterus causing distention of the abdomen. The bacteria release toxins that are absorbed into circulation. These dogs often become severely ill very rapidly. They are anorectic (off food), very listless, and very depressed. Vomiting or diarrhoea may also be present.

Toxins from the bacteria affect the kidney's ability to retain fluid. Increased urine production occurs, and the dog drinks an excess of water. This occurs in both open- and closed-cervix pyometra.

How is pyometra diagnosed?

Dogs that are seen early in the disease may have a slight vaginal discharge and show no other signs of illness. However, most dogs with pyometra are not seen until later in the illness. A very ill female dog that is drinking an increased amount of water and has not been sterilised is always suspected of having pyometra. This is especially true if there is a vaginal discharge or painful, enlarged abdomen.

Dogs with pyometra have a marked elevation of the white blood cell count and often have an elevation of globulins (a type of protein produced by the immune system) in the blood. The specific gravity of the urine is very low due to the toxic effects of the bacteria on the kidneys. However, all of these abnormalities may be present in any dog with a major bacterial infection. If the cervix is closed, radiographs (x-rays) of the abdomen will often identify the enlarged uterus. If the cervix is open, there will often be such minimal uterine enlargement that the radiograph will not be conclusive. An ultrasound examination can also be helpful in identifying an enlarged uterus and differentiating that from a normal pregnancy.

How is pyometra treated?

The preferred treatment is to surgically remove the uterus and ovaries. This is called an ovariohysterectomy ("spey"). Dogs diagnosed in the early stage of the disease are very good surgical candidates. The surgery is only slightly more complicated than a routine spey. However, most dogs are diagnosed when they are quite ill so the surgery is not as routine as the same surgery in a healthy dog. Intravenous fluids are often needed before and after surgery. Antibiotics are also usually required for a period of time after surgery.

If your dog is a valuable breeding female then please contact your vet to discuss alternative options. They are not always successful, and can have some serious side effects.